Radio-amplifying circuits



Nov. 28, 1939. Re. 21,282

W. J. POLYDOROFF RADIO AMPLIFYING CIRCUITS Original Filed Aug. 26, 19293 Sheets-Sheet 1 llllllllll l l I500 500 A16.

FREQ unvc r ATTORNEYS Nov. 28, 1939. w. J. POLYDOROFF 'Re. 21,

RADIO AMPLIFYING CIRCUITS I5 Sheets-Sheet I5 Original Filed Aug. 26,1929 M I IINVENTOR [dd/m Pojydo 1% ATTORNEYS Reiuued Nov. 28, 1939UNITED STATES am: RADIO-WING crncm'rs Wladimir J. Polyiloroir, Wilmette,llL, aoslgnor to Johnson Laboratories, Inc., Chicago, 11]., a

corporation of Illinois Original No. 1,940,228, dated December 19, 103:,

Serial No, tion for 118,948

1'! Claims.

The invention relates to the use 01 iron or other magnetic materials inradio-frequency and other alternating current circuits. Moreparticularly, the present invention contemplates the use of suchmaterials in tuned radlo frequency amplifying circuits, although theparticular new instrumentalities to be described and claimed are notlimited in their advantageous application to this particular class ofapparatus.

As is well understood in the radio art, a tuned radio-frequencyamplifying circuit consists essentially of a relay device such as athermionic amplifying tube, and an electrically connected resonantcircuit consisting of inductance and capacity. This resonant circuit isthe portion of the radio-amplifying circuit m which the property ofselectivity resides, and it may therefore be referred to as theselective circuit, as distinguished from the complete amplifying circuitincluding the tube or relay.

Hitherto. many attempts were made to employ iron cores inthetransformers used in radio frequency, but owing to great lossesintroduced by the iron as then employed, efliciency was generallyimpaired. so that air-core coils and transformers are now exclusivelyused in the cases where relatively high-frequency oscillations, eithermodulated or not by voice frequencies, are to be selected and amplifiedby thermionic tubes and associated circuits.

The invention will be better understood it reference is made to theaccompanying drawings where Figure 1 represents a general circuitemploying thermionic tubes and embodying the present invention;

Figure 2 is a diagram showing the amplification 01. a single stage ofsuch a system;

Figure 3 is a diagram showing the resistance variations of variouscoils;

Figures 4. 5, 6, '7 show various modifications of the present invention;

Figure 8 shows one application of the present invention;

9 shows the amplification curve or one stage 01' the circuit, of Figure8;

Figures 10, 11, 12 and 13 show selectivity curves of amplifiers ofvarious designs;

Figures 14 and 15 show modifications invention; and

Figure 16 shows a tuning device including correlated elements.

It is usual practice to employ several stages of radio-frequencyamplification in cascade, as .shown on Figure 1, having variableinductances 61' the uniform amplification.

388,23 A ll lt 28, 1928. Applica- December 2, 1986, Serial No.

or capacities, or both, in the tuning circuits, so as to cover a certainband of frequencies, say from 1,500 to 550 kilocycles. Such a wide rangeof frequencies renders the amplifying circuits ineiilcient and dliferentin operation at difi'erent frequencies.

It is the object of the present invention to improve fidelity,selectivity and efllciency and to secure'uniiormity o1 amplification.

Mathematical analysis (Victor 0. Smith, Proc. 1. R. E. vol. 15, No. 6,June, 1927) shows thatthe amplification of tuned radio-frequencycircuits is represented by the ratio of output to input voltages:

providing the circuit is tuned to the resonance, and optimum couplingbetween primary and secondary circuits is obtained at each frequency.These iormulae prove that with fixed inductance La. in order to keep theamplification constant, the resistance R: of the tuned circuit, which ischiefly composed of the coils resistance, should change proportionatelyto the square of the frequency.

In the case of a fixed value of mutual inductance, M, the amplificationdecreases with increase of tuning capacity as represented by the curve a01 Figure 2, when the mutual inductance is adjusted for thehigh-frequency end of the frequency band. Mutual inductance can bechosen to be at the optimum value somewhere in the middle 01' thefrequency band as represented by the curve b of said figure. In thiscase, the circuits being over-coupled at high frequency andunder-coupled at low frequency, produce non- The above formulae alsoprove that in order to keep the mutual inductance at its optimum valuethroughout the frequency band, the resistance R: should be so changed asstill to be proportional to the square of the frequency.

Actual measurements 01 the resistance of an air coil or transformer,show that the coil changes its resistance with frequency changes, butnot as much as would be required to keep the amplification constant andthe mutual inductance at optimum." Curve 0 oi. Figure 3, shows theresist-h ance for a certain air coil, measured at diflerent frequencies,while curve b represents the resistance required to maintain saidresistance proportional to the square of frequency.

One object of this invention is to provide radiofrequency circuits withtransformers which will not be subject to the described deflciencies ofair coils, to thereby attain even amplification with optimum mutualinductance. It has been found that the use of finely powdered iron inthe fleldpf an air cell. will change the variation of the resistance ofthe coil relatively to variations in frequency. I

A low-resistance air coil was chosen. and its inductance was materiallyaugmented by powdered iron disposed within said coil. The actualmeasurements of resistance throughout the entire range of frequenciesutilized, shown by the curve b of Figure 3, indicate that the resistancechanged approximately nine times while the fre quency changedapproximately three times. Numerous measurements have verified the factthat the resistance of iron-core coils remains proportional to thesquare of the frequency, despite frequency changes.

Transformers having powdered iron cores,

.were connected with thermionic tubes and other elements of the circuitof Figure 1, and it was found that the amplification curve remainedsubstantially even throughout the entire range of frequencies, asrepresented by the curve 0 of Figure 2. Thus, a close agreement withtheoretical considerations was established. that is to say. that whenresistance varies as the square of the frequency. the amplification of atimed circuit remains constant and the mutual inductance adjusts itselfto optimum value.

The resistances of transformers having powdered-iron cores, extremelysmall at 550 k. c. and the lower requencies, it is possible to buildtransformers and coils designed for those low frequencies having an L/Rratio much greater than is practical if ordinary air coils are employed.Furthermore, it is possible to reduce the windings and thereby minimisethe size of radio-frequency transformers, thus eifectunting a saving ofspace.

There may be several embodiments of my ironcore coils and transformers,the simplest embodimentbeingshowninl'igure4whereinprimaryandsecondarycoils LI arewoundonaninsulatingtubelandpowderedim'nlispackedinside the tube 8. and the ends 8 of thetube are sealed.

Flgurebshowsschematicallyabinocularcdli wound on insulating tubes I,portions I of the powdered iron being separated by thin paper discs 0,to prevent readjustment of its particles and consequent packing andslight change in inductance.

Ironcorescanalsobemadebyminlngvariom adhesive and insulating compoundswith powdered iron, and giving these cores the desired shape with orwithout pressure. Also. certain other insulator such as was, persiiineand mineral oils. may be used. when melted and mixed with i on,Particles. while-hot manifest very small losses but, when cold andsolidified, increase the conductivity of iron cores thousands of timesand establish easy paths for eddy currents at high frequencies.resulting in a considerable increase in radio-frequency resistance ofcoils equipped with such cores. However, a cell having either a meltedor an unmelted core oiwax, without powdered iron, developedsubstantially no resistance in the coil.

gether, will maintain insulating films between the iron particles and,therefore. reduce resultant radio-frequency losses.

The definition "iron used in the specification should be applied to anyother metal or alloy having magnetic properties, such as silicon-ironpermalloy and nickel-iron. Various powdered metals were tested forradio-frequency transformers and inductances, and it was found that forthe most satisfactory results iron reduced by hydrogen, the particles ofwhich had been sifted through a screen of 300 meshes to the inch, shouldbe used for frequencies between 1500 to 1000 h. 0., but that powderscontaining coarser particles may be used for frequencies below 1000 k.c., and also that the fineness and the force of compression govern theradio-frequency resistance of the coil. Iron produced by hydrogen in theordinary way contains particles of varioussizessomeofwhichmayhetoolargeforusein the production of cores suitablefor use in radio frequency circuits. It is, therefore, n to eliminatethe largest particles. The insulating coat of oxide usually present onthe surfaces of iron particles, helps to reduce eddy-current losses.when silicon iron powder is used it is practical to chemically treat thepowder with a phosphoric acid solution which creates an insulating him.

When. in this specification, "powdered iron" is referred to. I meaneither incoherent mssses of finely-divided iron, or of finely-dividediron compressed into bodies in which the individual particles are heldtogether by an insulating binder, but the degree of com should not be sogreat as to cause the particles of powdered iron to touch each other andthus exclude-the insulating material which should separate them.

To obtain maximum gain in inductance, thus duetotheironcores,thelengthofscoflshould be preferably twice its diameter, and the wireshould be space-wound. such arrangement being shown in Figure 6, whereinll indicates a spacewoundwire, and H indicates the powdered iron core.The inductance may be further augmentediftheironeoreextendsaroundtheoutside of the coil in the form of cylinder if. It will benoted that a space isleft between winding llamithecoreextension",andthatthe turnsofwinding llarespacedfromthecore by an insulatingsleeve. Such arrangement of iron completely closes the magnetic linesaround the coil. forming an astatic coil. ironooresareemployedinthecoilsoftheclosedor semi-closed magnetic field type,the original astaticproperttesofsuchcoilsaregreatlyenheneed. While thepowdered-iron core substantially doubles the individual primary andsecondaryinductances of a transformer, it increases the mutualinductance between the windings four orilvetimes.Thisphenomenonisespecisllyadvsntageous when a very ti ht coupling isrequired. or when long solenoids areemployed for Anotheroblectoitheprsssntinventlonis timearadiorfrequencycircuitinanemsimpleandeilleientmannenamovsblepowderediron through each selective circuit.Referring back to core disposed in the field of a coil being employedfor tuningpurposes. Depending on the amount of the iron powder insertedin the form of a core, the self-inductance of a coil may be increasedfour and even six times with a resulting increase in radio-frequencyresistance.

Figure 7 shows a binocular transformer ll, having a core ll which can bemoved in and out to obtain variations of self-inductance and mutualinductance. This device is capable of tuning the circuit to a desiredfrequency when connected with tubesand associated circuits such as shownin Figure l, or such'as are shown in Figure 8 wherein a radio-frequencychoke amplifier is represented. In this figure are shown thermionictubes, It and I0, acting as radio-frequency amplifiers, a detector tubel'l, choke coils ll having powdered iron movable cores it, suitableresistances 20, coupling condensers 2|, a telephonic receiver 22, and aplate battery 23, filament-heating means being omitted for simplicity.In this system it is possible to work the amplifier at its fullefilciency throughout a given range of frequencies by moving iron coresinward or outward. The amplification per stage is shown by curve a ofFigure 9. Core movements can be made simultaneous with the movements ofthe input selector, which selector is usual to secure the necessaryselectivity for wave lengths of different broadcasting stations.

When the selecting of a signal accompanies amplification, as in thecascade radio-frequency amplifier shown in Figure l, the ability toselect is called "selectivity" of tuned circuits. In an ordinaryair-core transformer associated with a resistance of the circuit varyingfrom 7 to 4 ohms,

are shown in Figure 10, wherein, the amplification is plotted againstkilocycles vi?! of resonance. Curve 0. is taken at a frequency of 1400k. c., curve b at 100 k. c., and curve c at 600 k. 0. Vertical lines (1and a are drawn at k. c. of! of resonance and represent interferingadjacent stations. Curve a shows inadequate selectivity due to highresistance of the circuit and to lack of capacity. As frequencydecreases, the resistance decreases the result being sharpening of thecurves b and c representing selectivity. By decreasing the inductanceand the losses in the circuit and increasing the initial amount oftuning capacity, it is possible to obtain sharper curves as shown inFigure 11. These three curves a, b and 0, represent a very satisfactoryselectivity, the amplitudes, as shown, being different because ,of fixedmutual inductance. The curves of Fig. are 12 represent the selectivityobtained from a transformer, equipped with a fixed powdered-iron core ashereinbefore described.

As the radio frequency signal is usually modulated by voice frequencies,three frequencies 7, fo-fv, and 10+! where In is carrier frequency,

Iv is voice frequency, have to be through a selective circuit withsubstantially equal intensities in order to avoid distortion. To secureintelligible audio signals, it is usual to modulate carrier frequencywith voice frequencies ranging from 0 to 5000 cycles, and, therefore,selective circults should be capable of mssing a band of frequencies l0kilocycles wide, to obtain the fidelity of reproduction. 'lwvo verticaldotted lines It and k in Figures 10, 11 and 12, represent the limits 0!s audio-frequency modulations to be passed Figure 10. one can easilyperceive that curve a shows almost perfect fidelity, curve b showsslightly distorted fidelity, the extreme side bands being attenuatedabout as compared with carrier frequency, and curve c shows 50%attenuation of its side bands and, therefore, introduces distortion.Curve 1: of Figure 11 shows good fidelity, but curves b and 0 showdistortion. Comparison of thesecurves with curves obtained by the use ofpowdered-iron core transformers, shows that all of the curves of Figure12 have very good fidelity, and poor selectivity. It is thereforeessential for good selectivity and fidelity, throughout the entirefrequency range to combine theselectlvity of a low-loss high-capacitycircuit at highfrequency with the selectivity and fidelity obtained bypowdered-iron cores at low frequency.

An amplifier was constructed with low-loss, low-inductance coils and amovable powderediron core and included in the circuit shown by Figure l.Tuned to high-frequency signals, such as 1500-1200 k. c., said core wasentirely withdrawn and the amplifier then developed the characteristicsof the curve a of Figure 11. From any high-frequency between 1500 and1200 k. c., to 550 k. c,, said core was gradually moved inside the coil,and, due to increases of self and mutual inductances and ofradio-frequency resistance, the curves became broad. The resultant groupof curves, taken at three different frequencies, is separatelyrepresented in Figure 13 and shows substantially the same selectivityand fidelity throughout the entire range of frequencies.

As it is customaryto express the selective properties in terms of bandwidths in kilocycles at half amplitude, I have chosen to call thisquantity the selectance and have used this word in this sense in theappended claims. As determined from Figure 13, the selectance is of theorder of 30 k. 0., slightly varying at three investigated frequencies.Theoretical analysis of a resonant circuit indicates that selectanceexpressed in band width is directly proportional to .where R and L are,respectively, resistance and fact that the selectances are substantiallyequal at three investigated frequencies, indicates that was keptsubstantially constant.

The equal amplifications represented in Figure 13 at three differentfrequencies, are easily explained if reference is made to Figure 14wherein one amplifying stage is shown with a tuned circuit 24 directlyconnected with the plate of a thermionic amplifier, said circuitconsisting of an inductance made variable by an iron core and anadjustable condenser 20, the output voltage of said amplifier being fedto a succeeding thermionic amplifier through a condenser and a gridresistance 21. Figure 15 shows essentially the same circuit 2| at M,with the exception that output voltage is fed through an additionalwinding unitariiy coupled, to the inductance of the tuned circuit ll.

The amplification may be theoretically expressedas R. withtheresultantlteand constant.

In case of simultaneous variation of capacity and inductance, theamplification of such a circmtcanberepresentedbytheabovctormulaemodified as follows:

and

. "neg.-

whei'e e|=2rf and where the ratio isthedynamicresistanoeoithecircuitatresonance. Inadditiontothecbangeoivalucoi'lsandcahslsaisovadcdbythemovementor the iron core. By properly thelowlom coils. and properly choosing the quantity.

ilnenemoiandpresmreontheiromaswellas adjusting the movement the ironcore in con- Junction with other tuning elements. amplifies, tion may bekept constant. 1

Using loose coupling between the primary and secondary circuits, it wasfound favorable to vary the mutual inductance to a verylarge extent, sothat at high irequencles the primary and secondary circuitswereunder-coupled while at low frequencies they were over-coupled. thesevariations being Pro ced automatically by the said movements of the ironcore.

when movable iron cores are used for timing purposes in coniunction withother variable devices, such as variable condensers. variableinductances, variometers and the like. the movements oi iron coresshould be correlated with the movements of said variable devices. It isprefgmovable necticnwith amplifying circuits,suchssshown inriguresi, 14and ifi hvsriablecondeneerlt havlngatatimiary plates 32 and rotary plate88.

carries a grooved cam 34 ilrmly connected with theshart II. A level-1i.engaging the cam groove,

actuatcs a vertical rod 31 towhich a powderediron core is fixed. Atransformer I, which may be an impedance coil, telescopically receivessaid core 88. when the condenser plates are retated for tuning purposes,the cam 34, its lever II and the vertical rod 81 are set in motion, sothat the core 8| travels inward and outward relatively to the coil 30.when the condenser plates 81, are out, the core 18 is all the way out,which position corresponds to a higher-frequency limit oi the circuit.when the plates II are in, the core II is in the coil and this positioncorresponds to a lower-frequency limit. The movements of the core inrelation to the rotation of the condenser plates is governed by thecurvature of the cam 34. It is possible to move the core 88proportionally to the angular movement of the rotary plates, in whichcase the condenser plates may be so shaped as to give the desiredcapacity variations.

However, it is preferable to employ semi-circular platesproducingstraight-line capacity variations, and to so choose thecurvature 9! the com 8 that the speed of the core will be'acccleratedrelatively to that 91 the rotary plates 88 of the condenser. This train01" elements admits of a slow movement of the core 38 when said platesare having their initial angular motion, but causes, a gradualacceleration oi'the speed or the core 88 which reaches its maximum whenthe 'tuned solely by capacitance variation and of low inherenthigh-irequency'resistancc at frequencles within the range, an externalcondenser of appropriately high capacitance connected across said coil,the electrical values of said coil and said condenser being such as togive said resonant circuit a iavorable ratio oi. inductance toresistance at a particular frequency at the upper end or the range andto resonate at said frequency,

and means comprising a compressed ferromagnetic core body 10f tuningsaid resonant circuit to a materially lower irequency m the lower end orthe range and" for producing resistance increases in said resonantcircuit to substantially maintain said ratio, as the core body isdisposed within said cell, said core body having insulated magneticparticles 0! such quality, quantity, sizes,

and nature oi insulation and being so compressed tha't sald amplifyingcircuit has a resonant gain and selective properticssubstantially thesame as when said core body is withdrawn.

2. A high-irequency selective resonant circuit for use over a range offrequencies, such as 600 to M00 kiiocycles, including a condenser oirelatively higher capacitance and a coil oi" relatively lower inductancethan in conventional resonant circuits tuned solely by capacitancevariation, said cell having low inherent high-frequency realliance atfrequencies within the range, theelectricalvaluesotsaidcoilandsaidcondenserbeing anasa such as to givesaid'circuit a favorable =atio of quencies within therange, an externalcondenser inductanceto resistance at a particular frequency at the upperend of the range and to resonate at said frequency, and means comprisinga ferromagnetic core body having insulated magnetic particles and beingmovable relatively into said coil and whose resistance-increasing effectis sub stantially equal to its inductance-increasing effect, by reasonof the correlation of the quality, quantity, sizes and nature ofinsulation of said particles, for tuning the circuit, by movement ofsaid core body into said coil, to a materially lower frequency in thelower end of the range, whereby said ratio of inductance to resistance,and hence the resonant gain and selectivity of said circuit, issubstantially maintained.

3. That method of tuning a selective high frequency circuit havinginductance, capacity and resistance and having desired characteristicsat a'given frequency, which consists in simultaneously varying saidinductance and said resistance of said selective circuit by magneticmeans comprising a magnetic body having insulated magnetic particles soas to resonate the circuit to a substantially different "frequency whilemaintaining saiddesired characteristics.

4. That method of tuning a selective highfrequency system, having-aplurality of resonant circuits each including inductance, capacity andresistance, which consists in simultaneously varying said inductance andsaid resistance in said I resonant circuits, by magnetic meanscomprising a magnetic body having insulated magnetic particles, tothereby tune said system from an upper frequency to a lower frequencywhile maintaining the resonant response of the system substantially thesame at both of said frequencies.

5. A radio-frequency amplifying circuit including a vacuum-tube relaydevice and a selective resonant circuit operable over a range offrequencies, such as 600 to 1400 kilocycles, electrically connected toworking terminals of said relay device and having a coil of relativelylower inductance than in conventional resonant circuits tuned solely bycapacitance variation and of low inherent high-frequency resistance atfrequencies within the range, an external condenser of appropriatelyhigh capacitance connected across said coil, the electrical values ofsaid coil and said condenser being such as to give said resonant circuita favorable ratio of inductance to resistance at a particular frequencyat the upper end of the range and to resonate at said frequency, andmeans comprising a compressed ferromagnetic core body for tuning saidresonant circuit to a materially lower frequency in the lower end of therange and for producing resistance increases in said resonant circuit tosubstantially maintain said ratio, as the core body is disposed withinsaid coil, said core body having insulated magnetic particles ofpowdered iron of such quality, quantity, sizes, and nature of insulationand being so compressed that said amplifying circuit has a resonant gainand selective properties substantially the same as when said core bodyis withdrawn,

6. A radio-frequency amplifying circuit including a vacuum-tube relaydevice and a selective resonant'circuit operable over a range offrequencies, such as 800 to.1400 kilocycles, electrically connected toworking terminals of said relay device and having a coil of relativelylower inductance than in conventional resonant circuits tuned solely bycapacitance variation and of low inherent high-frequency resistance atfreof appropriately high capacitance connected across said coil,theelectrical values of said coil and said condenser being such as to givesaid resonant circuit a favorable ratio of inductance to resistance at aparticular frequency at the upper end of the range and to resonate atsaid frequency, and means comprising a compressed ferromagnetic corebody for tuning said resonant circuit to {a materially lower frequencyin the lower end of the range and for producing resistance increases insaid resonant circuit to substantially maintain said ratio, as the corebody is disposed within said coil, said core body having insulatedmagnetic particles of hydrogen iron of sizes small enough to passthrough a screen having 300 meshes to the inch, and of such quantity andnature of insulation and being so compressed that said amplifyingcircuit has a resonant gain and selective properties substantially thesame as when said core body is withdrawn.

7. A high-frequency selective resonant circult for use over a range offrequencies, such as 600 to. 1400 kilocycles, including condenser ofrelatively higher capacitance and a coil of relatively lower inductancethan in conventional resonant circuits tuned solely by capacitancevariation, said coil having low inherent high-frequency resistance atfrequencies within the range, the electrical values of said coil andsaid condenser being such as to give said circuit a favorable ratio ofinductance to resistance at a particular frequency at the upper end ofthe range and to resonate at said frequency, and means comprising acompressed ferromagnetic core body having insulated magnetic particlesand being movable relatively into said coil and whoseresistanceincreasing effect is substantially equal to itsinductance-increasing eifect, by reason of the correlation of thequality, quantity, sizes and nature of insulation of said particles, andthe degree of compression of said core body, for tuning the circuit, bymovement of said core body into said cell, to a materially lowerfrequency in the lower end of the range, whereby said ratio ofinductance to resistance, and hence the resonant gain and selectivity ofsaid circuit, is substantially main-- 8. A high-frequency selectiveresonant circuit for use over a range of frequencies, such as 600 to1400 kilocycles, including a condenser of relatively higher capacitanceand a coil of relatively lower inductance than in conventional resonantquantity, sizes, and nature of insulation of said particles, for tuningthe circuit, by movement of said core body into said coil, to amaterially lower frequency in the lower end of the range, whereby saidratio of inductance 'to resistance, and hence the resonant gain andselectivity of said circuit, is substantially maintained.

9. A high-frequency selective resonant circult for use over a range offrequencies, such as 600 to 1400 kilocycl'ea including acondcnser ofrelatively higher capacitance and a coil of relatively lower inductancethan in conventional resonant circuits tuned solely by capacitancevariation, said coil having low inherent high-frequency resistance atfrequencies within the range. the electrical values of said coil andsaid condenser being'such as to give said circuit a favorable ratio ofinductance to ruistance at aparticular frequency at the upper end of therange and toresonate' at said frequency, and means comprising acontinued f core body having insulated hydrogen-iron particles oi sises10. A high-frequency selccti've resonant"circuitforusecyerarangcoffrequencieaswchas 600 to 1400 kilocycles.including an adjustable external condenser of relatively highercapacitance and a low-loss space-wound solenoids] coil of length not lmsthan twice its diameter, and of relatively lower inductance, than inconventionai resonant circuits tuned solely by capacitance variation,the electrical values of saidicoil andsaidcondenserbeingsnchastogivesaidci'rcuit 8 favorable ratioofinductance toresistdice at a particular frequency at the upper end ofthe range and to resonate at said frequency. and means comprising acompressed ferromagnetic core body having insulated magnetic particlesandofadiameferandlengthclolcly l flto the internal diameter andlengthofsaid coil and being movable relatively into said coil and whoseresistance-increasing effect is substantially equal to itsinductance-increasing effect, by reason of the correlation of thequality. quantity. sizes, and

nature of imuiatlm of said particles, for tuning the circuit, bymovement of said core ody into said coil. to a materially lowerfrequency in'the lower end of the range. whereby said ratio ofinductance toresistance, and hence the resonant gain and selectivity ofsaid circuit; is substan V tially maintained.

ii. That method of tuning and controlling a selective high-frequencyresonant circuit over a rangeoffrequencieasuchasllooto iiolihilocycles,said circuit having. inductance, capacitance and resistance and afavorable ratio of inductance-to-resistance characteristic at a givefrequency at the upper end (if the range. whi consistsin employingrelatively higher capacitance and relatively lower inductance than inconventional resonant circuits tuned solely by capacitance variation,and with the inductance of low inherent high-frequency resistance, tosecure said favorable ratio of inductance to resistance in said circuitat said frequency and to resonate at said frequency: tuning said circuitto amateriallylowerfrcquencyinthelowerendof the rangebyf 'theinductancethereof; and simul eously ferromagnetically introducing substanproportional increases in the high-frequency resistance of said circuit,to substantially maintain said ratio ofinductancetoresistanccinsaidcircuitinthe lower end of the whereby theresonant gain and selectivity of said circuit are each substantiallymaintained same at both said frelower frequencies, by employingrelatively higher capacitance and relatively lower inductance than inconventional resonant circuits tuned solely by capacitance variation'and with the inductance of ,low inherent high-frequency resistance. tosecure a favorable ratio-of inductance to resistance in each of saidcircuits at a frequency at the upper end of the range, and to resonateat said frequency: tuning each of said circuits to a materially lowerfrequency in the lower end of the range by fetically increasing theinductance thereof. and simultaneously ferromagnetically introducingincreases in the high-frequency resistances of said circuits tosubstantial- 1y maintain said ratio of inductance to resistance in eachof said circuits, whereby the resonant gain of said system issubstantially maintained.

18,.i'hat method of tuning and controlling" a high-frequency selectivesystem over a range of frequencies. such as 600 to .1400 kilocycles.ineluding a selective rwonant circuit having inductance, capacitance andresistance and a favorable ratio of inductance-to-resistance at a 7given frequency at the upper end'of the range, which consists inemploying relatively higher capacitance and relatively lower inductancethan in conventional resonant circuits timed solely by capacitancevariation, and with the inductance of low inherent high-frequencyresistance, to secure said favorable ratio of inductance to resistancein said resonant circuit at said frequency and to resonate at saidfrequency; inductively associating a winding with the said inductance tocouple said inductance to an external circuit; tuning said resonantcircuit to a materially lower frequency in the lower end of the range byferromagnetically increasing the inductance thereof, and simultaneouslyferromagnetically introducing in in the high-frequency resistance ofsaid circuit to substantialb maintain said ratio, and varying thecoupling between the associated winding and the said inductance, wherebythe selective properties of said system are substam tialiy maintained.

14. A radio-frequency amplifying circuit including a vacuum-tube relaydevice and a seiective resonant circuit operableover a range offrequencies, such as 600 to 1400 kilocycles, electrically connected toworking terminals of said relay device and having a coil of relatlvelylower inductance than in conventionalresonant circuits tuned solely bycapacitance variation, and of low inherent high-frequency resistance atfrequencies within the range; an external condenser of appropriatelyhigh capacitance connected acrms coil. the electrical values of saidcell and said condenser being such asto give said toce at a particularfrequency at the circuit a favorable ratio of inductance upper end ofthe range and to resonate at said frequency, a winding inductivelyrelated to said coil to couple said amplifying circuit to an externalcircuit, and means comprising a compressed ferromagnetic core body fortuning said resonant circuit to a materially lower frequency in thelower end of the range, for varyingthe coupling between said winding andsaid coil, and for producing resistance increases in said resonantcircuit to substantially maintain said ratio. as the core body isdisposed within said coil, said core having insulated magnetic particlesof such quality, quantity, sizes, and nature of insulation and being socompressed that said amplifying circuit has resonant gain and selectiveproperties substantially thesame as when said core body is withdrawn.

15. A high-frequency selective resonant circuit for use over a range ofrrequencies, such as 600 to 1400 kilocycles, including'a condenser ofrelatively higher capacitance and a coil of relatively lower inductancethan in conventional resonant circuits, tuned solely by capacitancevariation, said coil having low inherent high-frequency resistance atfrequencies within the range, the electrical values of said coil andsaid condenser being such as to give said circuit a favorable ratio ofinductance to resistance at a particular frequency at the upper end ofthe range and to resonate at said frequency. and means comprising aferromagnetic core body having insulated magnetic particles and beingmovable relatively into said coil and whose resistance-increasing effectis at the most equal to its inductance-increasing effect,

by reason of the correlation of the quality, quantity, sizes, and natureof insulation of said particles, for tuning the circuit, by movement ofsaid core body into said coil, to a materially lower frequency in thelower end of the range, whereby said ratio of inductance to resistance,and hence the resonant gain and selectivity of said circuit, is notdecreased.

16. A radio-frequency amplifying circuit ineluding a vacuum-tube relaydevice and a selective resonant circuit operable over a range offrequencies, such as 600 to 1400 kilocycles, electrically connected toworking terminals of said relay device and having a coil of low inherenthigh-frequency resistance at frequencies within the range, an externalcondenser connected across said coil, the electrical values of said coiland said condenser being such as to give said resonant circuit afavorable ratio of inductance to resistance at a particular frequency atthe upper end of the range and to resonate at said frequency, and meanscomprising a compressed ferromagnetic core body for tuning said resonantcircuit to a materially lower frequency in the lower end of the rangeand for producing simultaneously resistance increases in said resonantcircuit to substantially maintain said ratio, as the core body isdisposed within said coil, said core body having insulated magneticparticles 01 such quality, quantity, sizes, and nature of insulation andbeing so compressed that said amplifying circuit has a resonant gain andselective properties substantially the same as when said core body iswithdrawn.

17. A high frequency selective resonant circuit for use over a range offrequencies, such as 600 to 1400 kiiocycles, including inductance,capacitance, and resistance, said circuit having desired characteristicsas determined by its inductance to resistance ratio at a given frequencyat the upper end of the range and being resonant at said frequency, andmeans comprising a ferromagnetic core body having insulated particlesfor tuning said circuit to a materially lower frequency in the lower endof the range and for producing simultaneously resistance increases insaid circuit to substantially maintain said ratio whereby said circuitwill resonate at substantially different frequencies while maintainingsaid desired characteristics.

WLADINIIR J. POLYDOROFF.

CERTIFICATE OF CORRECTION. Reissue No; 21,282 November 28, 1959.

wIlADInIR J. POLYDOROFF;

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3,first column, line 1 1;, for "100 k. 0." read 1000 k. 0,; page Ly, firstcolumn, line 9, before the word "to" insert equal; and that thess'idLetters Patent should be read with this correction therein that thesame may conform to the record of the casein the Patent Office.

' signed and sealed this lth'day of Januarj, A. D. 19M).

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

